The involvement of polyamines in growth control of 3T3 and other cell lines will be examined. 3T3 cells respond to pituitary growth factors with a rapid induction of ornithine decarboxylase (OD), the rate-limiting enzyme in polyamine biosynthesis, and subsequent increases in the rates of RNA and DNA synthesis and cell division. These partially purified factors will be purified to homogeneity. There is data consistent with a specific inhibition of translation of the OD message by polyamines. Testing of this hypothesis will be conducted in vitro with a wheat germ protein-synthesizing system in which the synthesis of immunoprecipitable enzyme will be monitored. This will require the purification of the enzyme from 3T3 cells, a task considerably simplified by the very high specific activity of OD in stimulated cells. The half life of the enzyme decreases markedly upon stimulation. As cofactor dissociability has been implicated as a rate-limiting step in enzyme degradation, the involvement of pyridoxal phosphate in this half life change will be investigated. To investigate the possibility that polyamines can substitute for magnesium in vivo in 3T3 cells, variations in the intracellular concentrations of magnesium and polyamines in response to manipulation of extracellular magnesium will be monitored. The induction of polyamine synthesis in 3T3 cells by various agents has been found to be highly correlated with stimulation of RNA synthesis. The RNA produced after pituitary factor stimulation will be characterized kinetically on polyacrylamide agarose gels to determine if specific classes of RNA and/or maturation processes have been affected. The changes in RNA synthesized will be related to changes in the concentrations of polyamines determined by fluorescence analysis of dansylated derivatives. If indicated, the RNA synthesized by isolated nuclei will be analyzed similarly. The possibility of derangements in polyamine metabolism in mammalian cell mutants which are temperature sensitive for RNA synthesis will be investigated in attempts to identify a critical role for polyamines.